JOHANNESBURG  A conservation group said on Thursday there was little evidence to back the view that migrating wildfowl were spreading bird flu and said that eastern Europe's outbreak probably stemmed from poultry imports.

"As the year draws to a close, millions of wild birds have flown to their wintering sites across Asia, Africa, Europe and the Americas without the widely predicted outbreaks of H5N1 bird flu associated with their migration routes," BirdLife International said in a statement.

"The most obvious explanation is that migrating wild birds are not spreading the disease," said Dr Michael Rands, Director and Chief Executive of BirdLife.

However, animal health experts said they could not rule out the involvement of wild birds in spreading the virus across Asia and into eastern Europe.

"It is now not possible to exclude the role of some aquatic wild birds in the transmission of the current Asian strain H5N1 to domestic birds close to the migratory routes of these wild birds," Bernard Vallat, Director General of the World Organisation for Animal Health (OIE), told Reuters.

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The H5N1 bird flu virus has killed nearly 70 people in five Asian countries since 2003 leading to mass culls of birds.

NO "SMOKING GUN"

Officials say the H5N1 virus could spread to new countries through migratory birds from China, Mongolia, Vietnam and Russia -- which have reported major outbreaks.

The U.S.-based Wildlife Conservation Society earlier this year helped confirm that swans and other birds carried avian flu to a lake in Mongolia.

But BirdLife said no "smoking gun" had been detected among migratory wild birds in eastern Europe.

"The limited outbreaks in eastern Europe are on southerly migration routes but are more likely to be caused by other vectors such as the import of poultry or poultry products. The hypothesis that wild birds are to blame is simply far from proven," said Rands.

"Wild birds occasionally come into contact with infected poultry and die: they are the victims not vectors of H5N1 bird flu," he said.

The OIE's Vallat agreed that trade in birds could also play a role in the spread of bird flu.

"...the potential transmission of the virus through commercial and non commercial exchanges of live domestic birds including pets and products may also play an important role," he added.

Vallat did not want to see a mass cull of wild birds.

"The destruction of wild birds to avoid transmission to domestic birds is strongly not recommended because, among other things, it would lead to the dispersion of birds and would facilitate the spread of the virus worldwide," Vallat added.

BirdLife said banning the movement of poultry and related products from infected areas and restricting the global trade in captive birds were the best prevention methods.

The H5N1 strain has not been detected in Africa yet but experts say uncovering it in the region's rural areas will be difficult because of poor logistics and already high mortality rates among the continent's backyard chickens.